The present invention relates to a magnetic disk drive, and more particularly to an improvement in positioning accuracy of a magnetic head with couple and disturbance occurring in seek operation of the magnetic disk drive.
In recent years, an improvement in recording density of a magnetic disk drive is required to increase the storage capacity thereof. For this purpose, it is important to increase the positioning accuracy of the magnetic head. However, there are various factors that obstruct the improvement in positioning accuracy. The obstruction factors include: a positioning error caused by the force of air during the rotation of a disk; a positioning error caused by vibrations of a mechanical system as a result of positioning operation of an actuator; and a positioning error occurring when vibrations are applied from the outside of the magnetic disk drive. In order to reduce these positioning errors, it is necessary to widen a control band of positioning control, or to reduce vibrations of the mechanical system itself.
Among them, problematic vibrations are the vibrations that are applied from the outside of the magnetic disk drive, and the vibration caused by “couple” occurring in the base as a result of the positioning operation of the actuator. For example, under the condition that a plurality of magnetic disk drives are placed in a case of a server, operation of other disk drives causes such disturbance. Although the access time is improved, in other words, although vibrations occurring at the time of seek operation increase in surrounding magnetic disk drives in a case, high-density devices produced in recent years have large problems including: requirements of improved positioning accuracy; the decreased stiffness of a case for storing magnetic disks as a result of cost reduction; and a low control band. Moreover, what becomes a problem in like manner is an in-plane rotation mode in which by the couple including reaction force occurring in a VCM at the time of the positioning operation of the actuator and thrust transferred from a coil to a pivot, the base vibrates as a rigid body at natural frequency with the stiffness of the case being used as a spring constant.
In the in-plane rotation mode of the whole magnetic disk drive as a rigid body, a position of a target track on a disk deviates in response to the rotation of the device as a whole. On the other hand, an actuator stays at the same position without rotating by the inertia. As a result, a positioning error occurs. As a method for solving this problem, patent document 1 (Japanese Patent Laid-open No. 2001-291363) provides a mechanism as follows: by use of a support member having a cylindrical or curved shape, flexibly supporting a head disk assembly (HDA) on the frame at an in-plane rotation frequency of about 20 Hz; and thereby separating the natural frequency from the frequency in the in-plane rotation mode in which the whole magnetic disk drive is used as the moment of inertia, and in which the stiffness of the case is used as a spring; isolating disturbance of the case from vibrations; and making it hard to excite residual vibrations caused by couple so that servo compression can be expected.